Electric furnace



Aug. 2, i938. R R. RHDGWAY ELECTRIC FURNACE Filed June 6, 1935 4Sheets-Sheet l s E m if;

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ELECTRIC FURNACE y Filed June 6, 1935 4 Sheets-Sheet 2 Au@ 29 w38o H. R.RHDGWAY ELECTRIC FURNACE Filed June 6, 1935 4 Sheets-Shes?I 4 w n, n M WPatented Aug. 2, 1938 UNITED STATES PATENT oFFlcE ELECTRIC FURNACEApplication June 6, 1935, Serial No. 25,244

8 Claims.

'I'he invention relates to electric furnaces, particularly of theresistance type and, with regard to its more specific features, to anelectric furnace having pressure molding apparatus.

One object of the invention is to provide a furnace which will operatecontinuously at temperatures up to 2500 deg. C. Another object of theinvention is to provide a low voltage carbon resistor furnace which Willoperate at a high power factor so that an electrical control oftemperature can be maintained where the wattage absorption of thefurnace is proportionate to the change of voltage and where the wattlesscomponent of the current is kept at a minimum. Another object of theinvention is to provide a carbcn resistor tube furnace adapted for largepower inputs manufactured of metallic parts yet having no appreciablepower losses from magnetic hysteresis and eddy currents. Another objectof the invention is to provide a furnace construction to receive aneasily replaceable tube resistor. Another object i the invention is toprovide a furnace construction adapted to insure long life to a tuberesistor. Another object of the invention is to provide a gas-tightcontainer for an loxidizable tube arranged so as to prevent destructionof the tube by reaction with air and at the same time providing forexpansion and contraction of the tube which occurs during heat- 30mg andcooling of the furnace. Another object of the invention is to providefor the maintenance of continuous electrical contact and constantcontact resistance with the resistor and at the same time permittingexpansion and contraction of the tube freely in the container shell.Another object of the invention is to provide a high temperature furnaceadapted for the maintenance of a long uniform temperature zone which isat the same time adapted to the application of mechanical pressure onthe furnace contents and the simultaneous exact measurement of thetemperature. Another object of the invention is to provide a furnacewhich will operate at a high degree of thermal efficiency whileconforming to the requirements of the other objects listed above.Another object of the invention is to provide an improved furnace forcarrying out the process disclosed in the copending application ofRidgway and Bailey, Serial No. 694,502 filed October 20, 1933. Anotherobject of the invention is to provide combined pressure apparatus andfurnace apparatus which may be easily and quickly manipulated forloading and unloading. Another object of the invention is to provide anelectric '5J furnace having a sufficient seal. Another object of theinvention is to provide a resistance type furnace in which adequateprovision is made for cooling the members that support the resistanceelement. Another object of the invention is to provide a furnaceconstruction of extremely low inductance as well as of low ohmicresistance. Another` object of the invention is to distribute thecurrent evenly around the electrodes in order to attain uniformtemperatures. Other objects will be in part obvious or in part pointedout hereinafter.

The invention accordingly consists in the features of construction,combinations of elements and arrangements of parts, as will beexemplified in the structure to be hereinafter described and the scopeof the application of which will be indicated in the following claims.

1n the accompanying drawings, in which is shown a preferred embodimentof my invention,

Figure l is a view partly in axial section and partly in elevation ofthe furnace and pressure apparatus;

Figure 2 is a view partly in end elevation and partly in cross-sectionalong the lines 2-2 of Figure 3;

Figure 3 is an axial' sectional view on an enlarged scale of one end ofthe furnace;

Figure iis a cross-sectional view taken on the line @-4 of Figure 3;

.Figure 5 is a cross-sectional view taken on the line 5--5 of Figure 3;

Figure 6 is a fragmentary enlarged sectional view on an axial plane of agland ring and associated parts;

Figure 7 is a plan view of a pressure plunger showing its articulationto a screw shaft;

Figure 8 is a cross-sectional View taken on the line 0--8 of Figure l;

Figure 9 is'a detailed sectional view of the bus bars and theirconnection to the furnace;

Figure i0 is an enlarged front elevation of the central' portion of thefurnace showing the sighting tube for an optical pyrometer andassociated structure;

Figure l1 is a fragmentary axial-sectional view illustrating a manner ofusing the furnace apart from the pressure apparatus;

Figure 12 is an isometric view of the entire apparatus.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

Referring rst to Figures l and l2, I provide a pair of standards 20, 20,as shown in Figure 1, which may be similar but oppositely oriented andIntersecting the standards 24, 23 at the plane marked by the lines 22,22 on Figure 12 are generally U-shaped supports 23 comprising planesheet metal ends 24. outside sheet metal plates 2l. and inside sheetmetal plates' 23, the latter being bent into circular cylindricalsegments, and either the plates 2l or 23 being bent around the tops oi'the U, and the entire structure constituting a support for a cylindricalfurnace from which it cannot accidentally roll on'. This structuredescribed is strong and rigid and of very low specific heat. The insidepair of sheet metal ends 24 may be integral with the corresponding sidesof the pyramidal standards 23 if desired, and the various parts may bewelded together, the entire frame structure being more clearlyunderstandable from inspection of Figure 12 than is possible by way ofverbal description.

Extending through the upper ends of the U-shaped supports 23 and alsothrough the lower portion of the supports are three supporting tubes 21.'Ihese tubes 21 lend further strength and rigidity to the supportingstructure; they also constitute a mounting for thrust members for thepressure apparatus to be described. These thrust members preferably takethe form of three tubes 28 which are slidable in the supporting tubes21.

yReferring now to Figure 8, resting on the inside cylindrical plates 23are chairs 33. 33 :in the form of inverted Us. There are a pair of thesechairs 30 in each support 23, thus making four in all, and upon theinclined tops thereof I alx insulating and heat-resistant pads 3l.

Resting on top of the pads 3| are a pair of aluminum cylinders 32 and 33connected together by ilanges 34 and 3l and bolts 3l. An insulatlng ring31 is interposed between the flanges 34 and 35, and as better shown inFigure 9 insulating sleeves 38 are provided surrounding the bolts 36. Asshown in Figures 1 and 12 a rectangular portion 39 is formed in theotherwise cylindrical wall of each cylinder 32 and 33, and through theopenings formed thereby access may be had to the interior of thecylinders as for the introduction of heat insulating material the natureof which will be presently described. Covers 40 normally cover theseopenings.

Referring now particularly to Figure 3, closing the otherwise open endof each cylinder are an nular end plates 4i. 'I'hese annular plates 4|may be made of aluminum or other suitable may terial and may be weldedto the cylinders 32 and 33 respectively. By the provision of aluminumcylinders partly closed by aluminum end plates, I have provided anon-magnetic material surrounding the central heating chamber of myfurnace, and at the same time the material is electrically conductiveand I use the cylinders 32 and 33 for passing a heavy heating currentinto the furnace by a cylindrical path, the advantages of. which willpresently be pointed out.

Referring now also to Figure 8, the annular plates 4I have integralcylindrical portions 43 geometrically projected from the inside boundingcircles of the plates. The portions 43 conmamas stitute supports for theheating resistance element and the electrodes. Slidably mounted in thecylindrical extensions 43 are cylindrical rings 4l having radial inwardextensions 43. One of the features of the invention is the provision ofmeans permitting the expansion and contraction of the heating tubehereinafter described without fracture thereof. Another feature of theinvention is the accomplishment of the foregoing with a gas-tight seal.I provide gland rings 41 which support the tube hereinafter referred toand also constitute the seal, expansion and contraction being taken careof by sliding of the rings 43 in the extensions 43. I have found,however, that .in order to prevent seizing of the rings 43 in thecylindrical extensions 43 it is desirable to water-cool the gland rings41. Accordingly these rings are water-cooled in a manner which will bemore fully pointed out hereinafter.

Referring now particularly to Figure 6, the construction of a gland ring41 and its connection to a cylindrical ring 4l is therein disclosed. Iprovide a pair of insulating rings 43 which, because of the hightemperatures encountered due to direct radiation from the heating tube,I prefer to make of mica, Transite or the like. The rings 43 are locatedon opposite sides of the radial inward extension 43 and bolts 43 extendthrough both rings 43, through the extension 44, and into the gland ring41 securing these parts together, but the gland ring 41 being insulatedfrom its support the cylindrical ring 43. I may also provide insulatingtubes 49a of mica or the like surrounding the bolts 49. Thus each glandring 41 is insulated from the aluminum shells 32 and 33 respectively.Excepting as hereinafter noted the furnace is symmetrical and every parton the left is duplicated by a part on the right and this holds true upto the bus bars and to the thrust ing elements of the pressureapparatus. so I V shall now continue to describe the left-hand end ofthe furnace using the singular excepting where there are a number ofidentical parts at each end. Referring now to Figures 1 and 3, thefurnace is a resistance type of furnace and the principal heatingelement thereof is a graphite tube 3l (there is only one such tube)which extends the length of the combined cylinders 32 and 33 andprojects slightly therebeyond at each end thereof. The graphite tube 50is supported by the gland ring 41 which has radial inward extensions Bidefining an annular space in which is located an annular ridge 52integral with the graphite tube 50, the lt being a loose one and thisconstruction constituting a labyrinth seal,.which is filled with thematerial which illls the cylinders 32 and 33. Thus this gland preventsentry of air into the furnace and at the same time supports the tube 50by loose connection in order to avoid breakage due to the high heatemployed and consequent expansion and warping of some of the parts.

The entire assembly constituting the tube l, the water-cooled gland ring41, and the cylindrical member 45 with its extension 46 is free to moveinside of the cylinder 43 as the graphite tube 50 expands under theinfluence of the heat generated therein, until the end of the ring 4lcontacts with limiting stops 53 bolted to the annular plate 4i, as shownin Figure 3; the gap 54 is large enough to take care of all theexpansion of the one-haii'. of the tube 50 that takes place in practice,while progressive creeping of the tube 33 electrodes 50, 50, 50 to eachend of the graphite tube 50. The electrodes 50 are segmental and ofidentical shape. Each one subtends an arc of approximately 120 deg., andas better shown in Figure 4, each is provided at its two endswithabutting flanges 6i, there being six such flanges for the threesegments collectively, and each set of three segments being flexiblyconnected together by bolts 62 passing through the flanges 5i and nuts63 which engage springs 6I; thus the segmental electrodes 60 aremaintained in firm contact with the tube 58 but when the diameter of thetube 58 increases on account of thermal expension, the electrodes expandwith it despite the fact that they are water-cooled. The electrodes 80are likewise formed with radial flanges 85,.each` one connecting a pairof anges 6I and displacing nearly one hundred and twenty degrees, and

the flanges 65 receive electric current from the4 cylinders 32 and 33,as will now be described.

Referring now to Figure 3, circumferentially around and upon the outsideof each of the cylinders 32 and 33, I solder copper plates 1l), and tothese plates 1li I bolt cable terminals 1I. preferably of copper, bymeans of bolts 1.2. The terminals 1I are mounted on the ends of cables13, the other ends of which extend into clamps 14 bolted to the flanges65. The cabl-es 13 are preferably of copper stranded cable, whichprovides a path of extremely low resistance for the current, also beingmechanically flexible, and the arrangement of these cables can beunderstood from reference to Figure 2 which shows twelve of them, fourextending to each electrode 50.

Referring now to Figures 1, 8 and 9, I provide upwardly extending wings15, integral with the flanges 34 and 35 respectively and the insulatingring 31 has a similar upward extension 15, and to these wings I fastenbus bars 11 and 18. The bus bars 11 and 18 are each of them branchingbus bars, and of slightly dierent shape and interlaced construction, asshown in Figure 1, and the form adopted insures that they and connectingleads or bars shall have low inductive reactance. As illustrated inFigure 9 in detail, copper plates 19 are soldered to the aluminum wings15 and the bus bars 11 and 18 are held to these copper plates 19 bymeans of four bolts 8| surrounded by insulating tubes 82 so that the busbars 11 and 18 are insulated from each other. Each bolt 8l is furtherprovided with insulating washers 83 and a nut 84 to complete theinsulation and to hold the parts together, this entire constructionbeing clearly shown in Figures 8 and 9. The bus bars 11 and 18preferably are made of copper, and I note that by providing copperplates soldered to the aluminum cylinders 32 and 33 and extensionsthereof, a very exc-client conducting path for the electric current isprovided, much superior to a direct contact between aluminum and copperwithout the soldering, as aluminum quickly oxidizes and the lm ofaluminum oxide found on the surfaces of exposed aluminum parts is not anextremely good conductor of electricity.

For molding boron carbide, in order to make articles thereof, I foundthat a temperature of around 2200 deg. C. had to be attained andtherefore a reasonable requirement of the furnace was that it should beable to operate continuously at temperatures up to 2500 deg. C. So faras I am at present aware, there are few materials which will withstandsuch high temperatures and the outstanding class of substances iscarbonaceous substances. I have found that electric furnace graphite ofthe brand known as Acheson's graphite .is the material which is mostreliable and constant in its properties within the temperature rangedesired for the resistance tube. Graphite, however, is not strong,relatively speaking, and therefore I make the tube of substantialcross-section, particularly as it is subject to mechanical strains inthe furnace. Graphite, however, has low electrical resistance whencompacted into a tube or the like and therefore a mechanically strongresistor tube will have lowl electrical resistance if the furnace is ofreasonable size. Therefore, in the case of a furnace large enough tomold fair sized articles, insomuch as there is a limit to the length ofthe furnace for mechanical reasons, the heating tube is of lowresistance, and `in order to attain high temperatures and reach them ina practical length of time, a high power (energy input rate) on theresistor is required. Because of the high power and the low resistanceof a practicable, resistor tube, high currents at low voltages areencountered. Since the R is so low the nductance L must be kept at aminimum value if high power factors are to result in the furnace.

This and allied objects ,of the invention are attained in theconstruction already described because the current paths in the aluminumshells 32 and 33 are not localized and the current path may be thoughtof as a series of elements along the cylindrical shell, the currentdirection being instantaneously always opposite to that in the carbonresistor tube. It will be observed that this feature would be attainedeven though the bus bars were not located at a mid point of the furnaceas disclosed. Insomuch as the heating tube 50 is as close to thealuminum shell as it may be consistent with heatl insulationrequirements, the magnetic flux induced by the current in one of theseparts does not give reactance to the flow of the current in the otherpart. Furthermore it will be seen that no continuous metallic currentpaths link the magnetic flux induced by the flow of the heavy currents.

Because of the radial distribution of the cables `13 around thecircumference of the furnace, only a fractional part of the currentlinks the flux induced in the space inside the cylindrical shells. tanceis attained which is theoretically possible. Although the cables 13 forma slight loop in extending to the water-cooled electrodes 60, vthey arequite short and I have found by experimentation -that the slightincreased voltage required for end-connections such as described is lessthan the losses incurred in having an actual sliding electrical contactin the position of the gland ring 41.

Although I prefer to make the cylinders 32 and 33 of aluminum because itprovides good electrical conductivity and mechanical strength with lowweight and low specific heat and absence of magnetic effects,nevertheless it should be noted that because the geometry of the furnaceis practically noninductive these cylinders might be made even of steelor iron without large losses. However, as stated, aluminum shells arepreferred.

Aand thus the furnace utilizes a very high per- Thus substantially theminimum induc-` centage of the kva. input in heating the resistanceelement 50. So far as operation of the furnace is concerned, the currentmight be direct current, but in commercial practice alternating currentis the one chiefly met with, and for high power installations at thelowvoltages it is the only one commercially practical, and therefore theelimination of inductive effects is of great importance from acommercial standpoint as even in the case of frequencies as low as 25cycles per second, with the amount of current which I found it desirableto use, inductive reactance is a factor of prime importance and theavoidance thereof measureably increases the efficiency of the furnace,and the accuracy of temperature control.

Considering now the cooling of the electrodes and the gland rings, andreferring first to Figure 1, I provide a water connection 9i) in theform of a union having a valve 9| which is connected by piping 92 to aT-union 93 where the Water branches, by way of feed pipes 94 extendingto each end of the furnace. At the exhaust end, I provide a union 96having a valve 91 which receives water from a pipe 98 extending from aT-union 99 that receives water from pipes |00 'extending to each end ofthe furnace. By means of the valves 9| and 91, the flow of Water may becontrolled, and by restricting the flow by the valve 91, the coolingchambers may be maintained full o'f water.' Distribution and return ofcooling Water is the same at each end of the furnace.

Referring now to Figure 3, it will be seen that the pipe `94 extendsupwardly beyond the axis of the tube 50 and there has a U-bend.Referring now to Figure 2, the delivery end of the pipe 94 is thereinshown and it is connected to a T- union |02 with branching extensions|03 and |04, the former leading up and the latter leading down. Thepiping is distributed around a circle which includes the electrodesdescribed, and still referring to Figure 2, at the top of the circle theextension |03 extends away from the plane of this view along a lineparallel to the axis of the furnace and branches into feed pipes |05 and|06.

'This connection is fragmentally shown in Figure 3, and as thereinshown, the feed pipe |05 extends downwardly and into one of the threeelectrodes 60, being the left-hand upper electrode as they are viewedinFigure 2. Referring now to Figure 2, the feed pipe |06 extendsdownwardly into the right-hand upper electrode 60. Water passages areformed in all three electrodes, a passage |01a in the left-hand upperelectrode extending downwardly through the radial fiange 65 and into thebase of the electrode G0, then along its entire length and outwardly.This passage |01a may be formed by milling radial slots in the electrodeat opposite ends of its deg. contour, then milling an arcuate slotconnecting these radial slots near the inner periphery of the segmentalelectrode, then closing the slots at the outside with welded segmentalrings and bars.

The feed pipe |95 leads to a similar passage |01b similarly formed inthe right-hand upper electrode 60. Passage |01a delivers water to adelivery pipe |09, and passage |01?) delivers water to a delivery pipeHB.

The downwardly extending feed pipe |04 extends backwardly and theninwardly to deliver water to a passage |01c the delivery end of which isconnected to a return pipe |2, thus cooling the lower electrode 60. Thepipe |09 extends radially. then axially, then radially again, andfinally into a segment coaxial with the furnace, and pipes ||0 and |2are Joined by a union to this segment |09, and thus water flows bothways in the segment |09 to a T-union III which connects to the exhaustpipe |00.

At the T-union |02 is a third pipe Il 5 extending in the third dimensionfrom pipes 04, |03 and |04, and this leads water to the gland ring 41 ina manner that can be better appreciated by reference to Figures 3, 5 and6. Figure 5 shows the pipe ||5, and Figure 6 illustrates one end of itwhich ext'ends through to the annular space Ill in the ring 41. Anexhaust pipe ||1, as shown in Figure 4, and also in Figure 3, leadswater to the union H3, and thus to the exhaust pipe |00. This gland ring1 is preferably a brass casting, and the passage l I5 may be made with acore.

Referring now to Figure 1, I provide at one end of the furnace movablepressure apparatus and at 'the other end thereof adjustable apparatus totake the thrust. Referring to the lefthand side of Figure l, the tubes28 support a spider |20 having parallel bores through three bosses |2|on the ends of the three arms thereof, and having a central hub. |22 inwhich is a nut |23 secured thereto. Extending through the nut |23 is ascrew shaft |24 on the left-hand end o! which is fastened a. hand wheel|25.

Referring now to Figure 3, the right-hand end of the screw shaft |24 isturned down, and fastened thereon by means of a pin I 26 is a collar 21having a boss |28 as better shown in Figure '7,

through which is a bore extending at right angles to the axis of theshaft |24. A plate |30 has a pair of ears |3| with holes aligning withthe hole in the boss |28, and plate |30 is pivotally mounted on thecollar |21 by means of a pin |32 extending through ears |3| and box |20.Extending forwardly from the plate |30 is a threaded support |33. Thescrew shaft |24 may be hollow, as shown, in order that it may be oflarge diameter without being too heavy.

Upon the threaded support |33 I mount a graphite pressure plunger |38,which has an internally threaded bore |31 for this purpose. The partsshown in Figure 7, with the exception of the screw shaft 24, areduplicated at the righthand end of the furnace, there being a secondgraphite pressure plunger |36 at the right-hand end of the furnaceconnected, however, to a piston rod |40. By reason of the articulationof the graphite plungers |36 as described, they may be swung throughapproximately deg. when the plungers are withdrawn from the furnace, andin order to facilitate this, desirably I provide a handle |4| fastenedto the pin |32 at each end, each pin |32 being secured to the ears |3Ias by means of cross-pins |42. To take the thrust on the screwshaft |24I provide transverse pins |43 extending through the bosses |2| and theshafts 28. It will be seen that when the parts are in the position shownin Figure 7, the thrust upon the plungers |36 is taken by the plate |30and transmitted to the collar 21 and thence to the screw shaft |24 atone end of the furnace, or to the piston rod |40 at the other end of thefurnace. For loading the furnace, the plunger |30 may be rapidlywithdrawn by means of the hand wheel |25 at the left-hand end of themachine, or by the pneumatically actuated apparatus at the right-handend of the machine, and by the provision for swinging the plungers |36through 180 deg. I am' enabled to make the entire apparatus more compactyet allowing ready access to the inside of the resistance tube 50.

Considering now the pneumatic pressure apparatus by which high pressuresmay be exerted upon a substance to be molded under heat and pressure inthe resistance tube 50, this apparatus may be supported upon the tubularshafts 23 at the right-hand side of the furnace as shown in Figure i.

Referring to that figure the piston rod |40 is connected to a piston |45in a cylinder` |46 which is supported by spiders |41 and |40 havingbosses |49 and |50 through which the tubes 20 pass. Longitudinal thrustis transmitted from the piston |45 and cylinder |46 to the rods 20through pins similar to the pins |43 and having the same function. Thecylinder |46 has cylinder heads |52 and |53, and a pipe |54 connects tothe left-hand end of the cylinder |46 through the cylinder head |52,while a pipe |55 connects to the right-hand end of the cylinder |46through the head |53. If desired a gauge |56 may be provided connectedto the right-hand end oi.' the cylinder |46 by means of a pipe |51. Eachof the pipes |54 and |55 leads to a triple valve |60 having an operatinghandle |6|, and a pipe |62 connects by Way of a valve |63 to piping |64leading to a source of air under pressure, steam under pressure or thelike. Triple valves being known, no cross-section thereof is shown, butin one position of the handle |6| air is admitted to the right-hand sideof the piston |45 while the left-hand end of the cylinder |46 isconnected to an exhaust pipe |65 which simply exhausts into the air. Inan opposite position of the valve handle 6| air or steam is directed tothe lefthand side of the piston |45, and the right-hand side of thecylinder |46 is connected to the exhaust |65. In a third, which is a midor neutral position of the handle 6|, the flow of air or steam is shutoi altogether by the valve |60, and both sides of the cylinder |46 areconnected to exhaust |65, or the parts connecting to the pipes |54 and|55 may be blocked. Various modications of this and various types ofvalves may be used, but by means of the handle |6| the piston |45 may bemoved to the right or left, and when moved to the left it may be thrustin that direction with great force, which is transmitted to the graphiteplunger |36.

As in the copending application previously referred to, an important usefor the furnace is to mold powdered boron carbide (B4G) under heat andpressure thereby forming a boron carbide article of great density,strength, and uniformity of crystalline structure. In the table below Igive a typical example of instantaneous values of electrical quantitiesfor a furnace constructed in accordance with the invention.

Considering now Figure 1, I have shown a graphite mold |10 in the centerof the furnace, and therein is the article |1| being molded under heatand pressure. Graphite plungers |12 are shown extending into the bore ofthe mold |10 and graphite spacers |13 connect the plungers .|12 to themovable plungers |36.

In order to conserve the heat generated in the furnace and in order toprevent the apparatus from becoming overheated, I ll the cylinders' 32and 33 with an .inert material, and inl order to avoid oxidation orother chemical aotivity this inert material should be, as nearly aspossible, of the same substance as the resistance element 50. Graphitebeing the substance which I prefer to use for the resistance element, Ihave found that powdered carbon, such as lamp black or the like is thesubstance which I prefer to use to confine the heat in the resistanceelement 50. Therefore I -ll the cylinders 32 and 33 with powderedcarbon, and this seeps into the space between the resistance element 50and the ridges 52 thereof and tl gland ring 41, and whatever oxidationtakes plates, takes place only at the opening of this gland. Any slightamount of air in the powdered carbon is converted into carbon monoxideor carbon dioxide and the reaction goes no further. I may charge thecylinders with carbon through the covers 40, and in order to facilitateremoval of all carbon therefrom I have provided screw threaded plugs |15in the bottom of the cylin- V ders 32 and 33.

It is one of the features of this invention that carbon black may beused without electrical leakage at the low voltage practically attainedthrough the specic non-inductive features, as the sole insulatingmaterial loosely packed inside of the cylinders. This carbon blackprovides heat insulation of great efficiency which is non-conducting atthe voltages used. It is well known that at temperatures as high as theoperating temperature of this furnace, heat losses by radiation areenormous. Carbon black acts as a radiation screen and at the same timeprevents conduction and convection. Any gas leaks in the joints of thefurnace permitting oxygen in the air to enter the compartment will bereacted upon by the finely divided carbonaceous filling material toabsorb the oxygen by combining with it. Furthermore, in case carbonmonoxide is formed and explodes, the covers 40 provide what is in thenature of a safety valve as they simply lift with the explosion whichthus does no damage to the-apparatus.

In the operation of this furnace it is desirable that a check be madeupon the heat developed Instantaneous values of electrical quantities 25cycles 00 cycles vPower Am- Miinput res Volts cmhms l k'wpe z x er. z XRF.

startofrun 61.2 5,880 10.6 1.71 1.8 .332 .98a 1.94 .79s .912 At moldingtemperature 8.28 1,600 6.2 3.235 3.25 .332 .995 3.33 .798 .971

In the above table Z and X are given in miin the graphite tube 50. Tothis end, and recrohms while P. F. represents power factor. ferring nowto Figures 8, 10 and 12, I provide The remarkable thing about theelectrical data is the high power factor achieved in this furnace usingsuch large currents at very low voltage. This is achieved by thefeatures hereinbefore described.

an orifice |60 in the tube 50 which is in line with the tapered' bore|8| in a graphite tube |82 "Whose axis is perpendicular tothat of thetube 50 and which is supported, as better shown in Figure 8, at theinside end by a countersunk portion in the side of the tube l0 and atthe outside end by means of a graphite plug |84 which is alsocountersunk to receive the end of the tube |82 as shown in Figure 8. Theplug |84 has a bore |85 and is in turn supported by a countersunkportion in a cylindrical block having a bore |88 which is in alignmentwith the bores |0| and |86. The block |58 may be made of suitableelectrical and heat insulating material. In Figure 8 I show the Athreebores |8|, |85 and |88 blocked by a plug which is inserted into acountersunk portion of the outside of the cylindrical block |88. |8| maybe made of the same substance as the block |88 and may be readilyremoved. When it is removed an optical pyrometer may be used todetermine the heat of the mold |10.

Referring now to Figures 10 and 12, it will be observed that the flanges34 and 35 merge into semi-cylindrical portions and |95 which support theblock |88 as shown. The semi-cylindrical portions |95 and |85 do notcontact each other but are separated by the insulating ring l1.

Referring now to Figure l1, I show a modification of my furnace in whichany article may be fused or otherwise heat treated but not underpressure. In this embodiment of the invention the furnace is of the sameconstruction as that already described, and the piston and cylinder unitas well as the screw shaft |24 and operating mechanism may be used forthe purpose of readily opening and closing the furnace, or lsimplifiedmechanism may be substituted therefor. In place of the graphite plungers|36 I provide graphite plugs 200 which are hollow the greater part oftheir length as shown in Figure 11, and have the inner ends of theirbores blocked bf; plugs 20|. The remainder of the interior of the plugs200 may be filled with lamp black 202 or other form of carbon or thelike. By this con'- struction I provide effective heat insulation forthe furnace at low expense. In the center of this furnace I have shown acrucible 205 representative of a container for an article or substancebeing fused under heat but not under pressure.

It is a feature of the invention that the total water-cooled area incontact with the graphite tube is maintained at alminimum. 'I'his isattained by the combination of the narrow sliding gland 41 and thenarrow electrodes 50. If the electrical contacts were allowed to slideto take care of expansion and contraction, much larger areas would haveto be provided and greater heat losses incurred.

There are definite practical limitations in the manufacure of graphiteresistors of great length in proportion to their cross-sectional area.Since it is desirable in a furnace of the type described to have thetemperature gradient fall continuously from the point of highesttemperature, which is in the center of the furnace, to the ends wherethewater-cooled electrodes are attached, a long zone of constanttemperature in the center of the furnace requires a tube which isrelatively llong in proportion to its cross-sectional area.

'I'he amount of the tube wasted on the ends for the electrodes and forthe glands should therefore be kept to the minimum, and by the provisionof narrow glands and electrodes a substantial saving and improvementhave been effected.

Considering now the operation of my furnace, having selected a suitablegraphite mold |10, and plugged up one end thereof with a graphiteplunger |12, I fill the mold from the other end This plug then insertthe other plunger |12. At this time the plunger |35 is withdrawn fromthe furnace and is away from the opening of the graphite resistance tube50. being swung back on its fulcrum |32. The piston |45 is to the rightso that the other plunger |35 is out of the tube 50 and it may also beswung out of the way. It may be desirable to cold-pressthe plungers |12against the boron carbide in the mold |10 with a slight pressure tofacilitate handling. Whether this is done or not, the entire unit may bereadily lntroduced into the graphite tube 50 and placed approximately inthe middle thereof, as by means of any long rod. Graphite blocks |13 arethen inserted in the furnace and moved up against the plungers |12. Theplunger |38 is now lowered and by spinning the hand wheel |25 it iscaused to enter the furnace.

By careful control of the handle |61, after lowering the other plunger|35 to horizontal position, this plunger may be now introduced into thefurnace. At this time the parts may be carefully watched so that theplunger |35 is moved just far enough to eliminate open spaces betweenthe various elements in the tube 50 without undue shock to the movingplunger. At this time it should be ascertained that the position of thetwo plungers |38 is approximately the same at both ends of the furnace,or if the positions of these plungers respectively are different,adjustment may be made by turning the hand wheel .|25. The valves 9| and91 should be now opened to insure the ow'of cooling water, and after thevalve 9| is opened wide the valve 81 should be closed slightly tosqueeze out air blocks.

The current may be now applied and the air should be now turned on bymeans of the valves |6| and |53 until the reading on the gauge |58 issuch as to give the desired pressure per square inch against the boroncarbide |1| being molded. As heretofore stated, all the factors of heat,pressure, time, and the like may be varied, and there will be acorresponding variation in the final article. However, results can beduplicated and the furnace is quite universal for the production of manydifferent types of articles. I contemplate that in many cases it will bedesirable to attach a pointer to the piston rod |40 which may extend toa scale marked on one of the rods 2B, for example. Any suitable type ofpointer or indicator may be used and it may be removable or adjustableor both.

An optical pyrometer may be used through the medium of the pyrometertube described, in order that the operator may control the temperatureas desired. In order to hasten the` cooling, a stream of water may beturned upon the outside of the cylinders 32 and 33. The pressure may be'reduced at an instants notice bymanipulation of the valve |6I.

The furnace described may be easily operated and controlled on accountof the means described for moving the plungers |36 and swinging them outof the way. Furthermore, a very high heat may be generated as alreadyindicated, and despite the high heat and pressure the graphite tube 50is not destroyed for itsl expansion is taken care of at the gaps 54 andthe pressure is confined to a single axis. In fact, it will be notedthat no couple whatsoever is generated by the pressure means employed,there being no component of force in any direction other than ahorizontal direction and the pressure as well as the thrust being alonga single axis. Furthermore, by reason of the distribution of the rods 28at equal distances from the axis of the tube 5D, all strains and forcesare balanced and there is no pressure against the cylinders 32 or 33 orany of the parts connected to the electrodes. Radial expansion of thegraphite tube can take place Without fracturing any part due to theexpansibility of the electrode structure. Furthermore, the flow oicurrent is cylindrical and radial thus substantially avoiding inductanceeffects. The insides of the cylinders 32 and 33 may be readily reachedat any time and it will be noted that the resistance tube, the heatinsulating structure and the electric current carrying structure, aswell as the water coolant connections, are freely suspended so as to bevirtually independent, in a structural sense, from the pressureapparatus. This further reduces undesired strains and stresses andalso'facilitates the dismantling of the furnace or the replacement ofparts whenever desired.

It will thus be seen that there has been pro- ,vided by this inventionan apparatus in which the various objects hereinbeforel mentioned aresuccessfully achieved. As various possible ern bodiments may be made ofthe above invention and as many changes may be made in the ein bodimentabove set forth, it is to be understood that all matter hereinbefore setforth or shown in the accompanying drawings is to be interpreted asillustrative and not in a limiting sense.

1. In an electric furnace, a casing, a tubular resistance element, asupport for the resistance element permitting slight axial movementthereof relative to the casing. a multi-segment electrode, radialiianges projecting from the opposite ends of each of the segments, andspring means holding said flanges together whereby to hold the segmentsrmly against the tubular resistance element yet allowing the resistanceelement to expand when heated. 1

2. In apparatus as claimed in claim l, the combination with partstherein specified of pipes to convey cooling medium to each of saidsegments.

3. In an electric furnace, a graphite tube, a pair of cylinderssurrounding said graphite tube, an insulating annulus separating saidcylinders, conductors to convey current separately to said cylinders,annular discs closing the ends of said cylinders, supporting sealingglands around said graphite tube in the form of hollow annuli supportedbysaid annular discs, separate annular electrodes clamped to said tube,and connections to lead current to the electrodes from said cylinders.

4. In an electric furnace, a graphite tube, a pair of cylinderssurrounding said graphite tube, an insulating annulus separating saidcylinders, conductors to convey current separately to said cylinders,annular discs closing the ends of said cylinders, supporting sealingglands around said graphite tube in the form of hollow annuli supportedby said annular discs, hollow annular electrodes, means to conveycooling medium to each of the four hollow annuli, and means to "conveycurrent from the cylinders 'to the electrodes.

5. In an electric furnace, a furnace casing, a support for said casing,pressure apparatus comprising a piston and cylinder unit and a thrusttaking unit, and connecting means between said piston and cylinder unitand said thrust taking unit supported by said support but free to movehorizontally independently thereof, whereby the casing is free from anyof the pres-Il sure forces.

6. In an electric furnace, a symmetrical, approximately cylindricalmetallic casing divided into two parts along a median line, a pair ofinterlaced parallel bus bars, one connected to each of said parts,annular insulation separating said parts, a central axial tube ofresistance material in said casing, radial electric connecting meansconveying current from the ends of the -respective parts of said casing,an electrode structure rigidly clamped to said tube and connected tosaid radial electric connecting means, and separate supporting means forsaid tube allowing sliding motion for expansion and contraction oi' saidtube, the construction constituting a substantially non-inductivefurnace having a high power factor by reason of non-inductiveness andrigidly clamped electrodes avoiding fracture of the tube by reason ofthe sliding action. y

7. In an electric furnace, a tube of fragile resistance material, a.furnace casing surrounding the tube, supporting means for the tubeconnected to the casing and supporting the tube rigidly in a radialdirection but permitting movement in an axial direction, a sealing glandaround said tube, a multi-section electrode clamped to said tubeincluding resilient means permitting the expansion thereof, andconductors connected to the electrode to convey current thereto, theresiliently pressed multi-section electrode constitutlng a goodelectrical contact without danger of fracturing the tube and a slidingsupport permitting expansion and contraction without fracturing the tubeyet sealing the inside of th furnace to prevent the escape of heat.

8. In apparatus of the class described, a cylinder and piston unit, aplurality of parallel rods. a spider connecting the cylinder to theplurality of parallel rods, a thrust taking member including a nut and ascrew, a second spider connecting the nut to the plurality of parallelrods, a furnace casing located between the rods and a. support for thecasing supporting also the parallel rods, the rods being free to move inthe direction of their axes independently of the casing and the support,whereby the rods take the pressure o! the piston and the strain is notexerted on the casing.

RAYMOND vR. RIDGWAY.

